The present invention relates to a puncture sealant for a rubber product such as a tire and, more particularly, to a cured puncture sealant for a tire, especially for a tubeless tire.
In general, it is said that a tubeless tire is relatively safe to puncture because when something like a nail has stuck in the tire, it is not easily removed and therefore a rapid loss of pressure does not occur. However, in practice, when driving a car having a tire punctured by a nail for a long time, especially at high speed, centrifugal force makes it easy to dislodge the nail, and once the nail is removed, a rapid air leak or puncture occurs and the car is in danger.
To prevent such danger, it is important to prevent a rapid air leak even if something like a nail is removed during operation of the tire. It has previously been proposed that a sealable composition be coated on the interior surface of a tire and cured, so that when the tire is punctured by something like a nail, the puncture is sealed at once to prevent an air leak and to maintain safe operation. For instance, as is shown in Japanese Pat. No. 324737, a sealant composition is applied on an interior liner of a tire during molding and is cured simultaneously when vulcanizing the tire; or after molding a tire, a sealant composition is coated on an interior surface by means of a spray.
The former technique has the disadvantages that the production is difficult and the balance of the tire after molding is not so good. In the latter technique, as is shown in U.S. Pat. No. 3,935,893, a large amount of solvent such as toluene must be used to lower the viscosity of rubbery material for making its spraying possible, because the rubbery material has a high molecular weight and, even if a relatively low molecular weight and low viscosity material such as polybutene is used together with it, it is impossible to lower the viscosity to the range capable of being sprayed.
Further, in such techniques, non-curing type sealants composed of polybutene and rubbery components have been proposed. However, these non-curing type sealants have the disadvantage that when the tire to which they have been applied is operated for a long time at high speed, the temperature is elevated and the sealant gradually moves to a center part of the tire to cause roughness thereon and, as a result, the balance of the tire becomes distorted and the sealing effect can not be obtained except at an isolated location. Moreover, these sealants have the disadvantage that when the tire is damaged by something like a nail during operation at a high temperature, the sealant having a lowered viscosity flows out through the leak to lower the sealing property. Also, adhesives using acrylic compounds have been proposed but their viscosity and sealing property are insufficient for a sealant to be applied on the interior surface of the tire.